This invention relates to grinding wheels and similar tools of abrasives and processes for making the same. The tools produced comprise cubic boron nitride (CBN) abrasive particles bonded by a resin matrix material wherein the CBN abrasive particles have a thick multilayer metal coating to aid retention within the resin matrix.
It is well known in the art that a coating of nickel or titanium on cubic boron nitride abrasive particles improves their retention in the resin matrices of abrasive tools such as grinding wheels. Loss of the coated particles typically results from (a) separation of the particle from the coating and (b) separation of the coated particles from the matrix. Loss of abrasive particles which have become worn and rounded is necessary so that the abrasive tool remains sharp with the exposure of new abrasives, otherwise the tool will become ineffective.
Titanium coatings are typically applied to CBN abrasive particles by conventional salt bath techniques, such as is described in U.S. Pat. No. 2,746,888. An alternative procedure is described in U.S. Pat. No. 4,399,167, wherein a mixture of CBN abrasive particles and titanium powder are heat treated. Both procedures provide a thin titanium coating which is believed to be chemically bonded to the CBN abrasive.
Nickel coatings are typically applied to the CBN abrasive particles in thick layers of up to 60 weight percent of the particle by electrolytic deposition, electroless deposition and/or vapor deposition techniques. While these coated CBN abrasive particles have provided good performance in tools such as grinding wheels, the loss of the CBN abrasive particles is considered premature. Improvements in particle retention are desired without detracting from the cutting performance of the abrasive tool.